Wellhead isolation mandrel with centralizing device

ABSTRACT

A wellhead isolation tool including a mandrel and a centralizing device. The centralizing device will align the tool so that the lower end of the mandrel sealingly engages the production casing. The mandrel has an open bore for allowing service tools to pass therethrough.

When a well is drilled to intersect a hydrocarbon-producing formation, it is often necessary to stimulate the formation to enhance the flow of hydrocarbons. Stimulation treatments generally include pumping of fluids under high pressure into a well and into a formation. The stimulation fluid may be, for example, an acid or a proppant containing fluid utilized for fracturing a formation. The stimulation fluids are in many instances corrosive and/or abrasive and can cause damage, sometimes irreparable damage, to wellhead equipment if the fluids are pumped directly through the wellhead into a well. To prevent, or at least limit damage to the wellhead, wellhead isolation tools are used. Wellhead isolation tools are designed to isolate the wellhead from the pressure, and corrosive/abrasive fluids.

Known wellhead isolation tools generally utilize a mandrel that is inserted through the various valves and spools of the wellhead. The mandrel will isolate the wellhead from the elevated pressures and from the stimulation fluids utilized during the stimulation process. The mandrel of the wellhead isolation tool is typically connected to a valve through which stimulation fluids will be pumped, and a bottom end of the mandrel is configured with a pack-off assembly so that a seal is provided between the lower end of the mandrel and either the production tubing or casing.

Typically, if other operations are to be conducted in the well, the wellhead isolation tool must be removed to allow the passage of service tools. For example, if it is desired to set a packer or bridge plug in the well above or below a previously perforated formation and perforate an additional formation in the well, the wellhead isolation tool must be removed and the bridge plug, or packer, along with the perforating device can be lowered into the well on a tubing or wire line. Once the bridge plug is set and the additional formation perforated, the service tools must be removed and the wellhead isolation tool reinserted for any stimulation of the formation. The process of removing the wellhead isolation tool, and then reinserting must be repeated any time tools must be lowered into the well to conduct downhole operations. The following U.S. published applications are examples of wellhead isolation tools: U.S. 2005/0217868 A1; U.S. 2003/0192698 A1; U.S. 2003/0221323 A1; U.S. 2003/0221838 A1.

There is a need for a wellhead isolation tool that will provide a proper seal to prevent damage to the wellhead and that will also allow for the passage of other service tools therethrough.

SUMMARY OF THE INVENTION

The wellhead isolation tool of the current invention is a self-aligning wellhead isolation tool that sealingly engages the production casing. The self-aligning wellhead isolation tool has a tubular mandrel with a centralizing device slidably mounted thereto. The tubular mandrel has a sealing system at or near the lower end thereof. The wellhead isolation tool may be inserted into the wellhead so that the tubular mandrel extends into the production casing and seals against the production casing. Thus, zones or formations intersected by the well may be stimulated by conducting stimulation fluid through the wellhead isolation tool into the desired formations. The seal between the wellhead isolation tool and the production casing will be such that the wellhead is protected against any abrasive and/or chemical damage since the stimulation fluid will not contact the wellhead.

The centralizing device and tubular mandrel comprise a centralizing apparatus. The centralizing device may comprise a plurality of bow springs slidably disposed about the mandrel and adapted to engage a wellhead interior thereby centralizing the tubular mandrel. Because the tubular mandrel is centralized, it may be efficiently inserted into the production casing. The tubular mandrel thus may be a relatively thin-walled mandrel that defines an open tubular bore through which service tools may be passed.

One or more zones may be stimulated through the wellhead isolation tool and thereafter service tools such as perforating devices and plugging devices (for example, packers, bridge plugs and other plugging devices) may be inserted therethrough so that other operations such as plugging and/or perforating in the well may be conducted. The service tools may be withdrawn through the wellhead isolation tool and stimulation procedures may then be conducted again.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows service tools positioned in a well.

FIGS. 2A-2D are cross-sectional views of the wellhead isolation tool extending into a production casing.

FIGS. 3A-3E are cross-sectional views of the wellhead isolation tool extending into the wellhead but withdrawn from the production casing.

FIG. 4 is a cross-sectional view of the centralizing device of the invention.

FIG. 5 is a perspective view of an additional embodiment of a centralizing device.

FIG. 6 is a cross-sectional view from line 6-6 of FIG. 5.

FIG. 7 is a cross-sectional view from line 7-7 of FIG. 5.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the drawings, FIG. 1 shows a well 10 comprising a wellbore 15 with a production casing 20 cemented therein which intersects formation 25. Perforations 30 may be provided by a manner known in the art to communicate formation 25 with well 10 so that hydrocarbons may be produced through the well. A tool string 31 is schematically shown disposed in well 10. Tool string 31 may include, for example, a sealing device 32 and a perforating device 34. FIG. 1 shows the tool string 31 lowered into well 10 on a wire line 36, but tubing such as jointed or coiled tubing may be used. Perforating device 34 may be, for example, a perforating gun of a type known in the art or, if the tool string 31 is lowered on a tubing, the sealing device may be of a type that utilizes fluid jets to perforate. Sealing device 32 may be a bridge plug, or other type of plug or packer known in the art for sealing the well to prevent flow therethrough. Apparatus known in the art to allow one-way flow may also be placed in the well, including, for example, but not limited to frac plugs. In FIG. 1, well 10 is shown intersecting an additional formation 38 which may be perforated to communicate the formation 38 with well 10 so that hydrocarbons therefrom may be produced up the well. Well 10 may intersect formations in addition to those shown.

Referring now to FIGS. 2A-2D, a cross section of a wellhead 40 is shown. Wellhead 40 defines a wellhead interior 42. A bit guide 44 is positioned in wellhead 40. A pair of seals 46 in a wellhead bore 48 seal against bit guide 44. Production casing 20 is suspended in well 10 with a casing hanger 50. Production casing 20 has outer surface 52 and inner surface 53 and will extend into the well to provide for the production of fluids therethrough. Outer surface 52 of production casing 20 is sealingly received in bit guide 44. The portion of production casing 20 shown in FIG. 2 extending from wellhead 40 may be referred to as a top casing, or top casing joint 54. Top casing joint 54 is received in an inner diameter 56 of bit guide 44, and sealingly engages seals 58. As is known in the art, production casing 20 extends into well 10 as depicted in FIG. 1. Surface casing 60 is suspended and extends from the wellhead 40 downwardly in well 10. Bit guide 44 is located in top head 62 and surface casing 60 extends downwardly from bottom head 64. Casing hanger 50 is seated in bottom head 64.

Wellhead isolation tool 68, which includes a centralizer apparatus 70 may be shown and described with reference to FIGS. 2A-2D and 3A-3E. Wellhead isolation tool 68 is a self-aligning isolation tool that will centralize in wellhead interior 42 of wellhead 40 so as to allow efficient sealing engagement with production casing 20. Referring now to FIG. 4, centralizer apparatus 70 comprises a mandrel 72 with a centralizing device 74 slidably disposed thereabout. Mandrel 72 has upper end 76 and lower end 78. A mandrel extension 80 is attached to upper end 76. Mandrel extension 80 is in turn connected to an upper portion of the wellhead isolation tool, which consists of valves and connections well known in the art. Mandrel 72 is preferably a thin-walled mandrel that defines a mandrel bore 82. Bore 82 is an open bore which provides for the passage of service tools therethrough so that wellhead isolation tool 68 may be utilized not only for treatment processes such as fracturing and acidizing, but as explained in detail hereinbelow, may be left in place when other service operations such as setting plugs, dropping balls or darts to engage seats or tools in the well, and perforating are conducted. Mandrel 72 defines an outer surface 84, with first or upper diameter 86 and second diameter 88 which is smaller in magnitude than upper diameter 86. A radially outwardly extending shoulder 90 is defined on first outer diameter 86. Shoulder 90 may be referred to as a bottom shoulder 90. A shoulder 92, which may be referred to as a top shoulder 92, is defined by a lower end 94 of mandrel extension 80. Shoulder 90 may comprise a ring connected to mandrel 72, or may be integral thereto.

Centralizing device 74 comprises an upper collar 96 and a lower collar 100 and includes a plurality of bow springs 98 extending between and connected to collars 96 and 100, respectively. Collars 96 and 100 may be attached to bow springs 98 by any means known in the art as well, such as fastening, or spot welding. Any desired number of bow springs may be included and in one embodiment, six bow springs 98 are equally spaced around the circumference of collars 96 and 100.

Diameter 88 has a magnitude such that it may be slidably received in production casing 20. The portion of mandrel 72 with outer diameter 88 may be referred to as lower portion 102. A sealing system 104 is operably associated with mandrel 72 such that when mandrel 72 is inserted into top casing 54 of production casing 20, a seal is created therebetween. Sealing system 104 is preferably positioned in a groove 106 on lower portion 102. Sealing system 104 comprises an annular ring 108 disposed in groove 106. Annular ring 108 has one or more sealing rings thereon, adapted and sized to sealingly engage inner surface 53 of production casing 20.

In the embodiment of FIG. 4, sealing rings 110 and 112 are disposed about, and preferably integrally formed with annular ring 108. The sealing rings may have increasingly larger diameters from the top down so that a diameter 114 on sealing ring 110 is smaller than a diameter 116 on sealing ring 112. Such an arrangement may be used, but is not necessary. Any number of sealing rings may be formed on annular ring 108.

The operation of the isolation tool 68 is as follows. After well 10 has been drilled and production casing 20 has been installed in wellbore 15, casing 20 will be perforated to create perforations 30 in a manner known in the art, so that formation 25 is communicated with casing interior 22. Formation 25 may then be stimulated by a treatment process such as acidizing or fracturing. If desired, wellhead isolation tool 68 can be installed prior to perforating formation 25, or between the initial perforating step and the stimulating process. Generally, prior to perforating, a plug, packer or other well sealing device will be set in the well below the producing formation 25.

When wellhead isolation tool 68 is inserted into the wellhead 40, it will be inserted so that sealing system 104 is received in top casing 54. Sealing system 104 shown in the preferred embodiment includes two sealing rings or seals 110 and 112 of increasing diameter from the lower end 78 toward the upper end 76 of mandrel 72. If desired, more or less than the two sealing rings may be used and one seal only may be used as well. Sealing system 104, and thus seals 110 and 112 are preferably an elastomeric material. Seals 110 and 112 may be swellable elastomeric materials which swell when exposed to a triggering fluid such as water, salt water, hydrocarbons, diesel fuel, kerosene or other chemical materials. Such materials are known and used for example in Halliburton Easywell™ Swellable Technology. Once mandrel 72 is sealingly inserted into production casing 20, stimulation procedures may be conducted. Because mandrel 72 seals inside production casing 20 below bit guide 44, the high pressure experienced during the stimulation procedures does not act upon any components of wellhead 40. Thus, wellhead 40 is protected from not only the high pressure but from the corrosive and/or abrasive effects of the fluids that might be utilized in acidizing or fracturing processes. After the initial formation 25 has been stimulated, it may then be desirable to perforate, stimulate and produce hydrocarbons from one or more additional formations intersected by well 10. The separate locations treated in the well may be referred to as zones, which may be separate formations intersected by the well, or which may be different zones of a single formation.

Because wellhead isolation tool 68 has a relatively thin-walled mandrel and because it has an open mandrel bore 82, wellhead isolation tool 68 does not have to be removed from wellhead 40 prior to passing service tools therethrough. Service tools such as, for example, perforating device 34 which may be a perforating gun lowered on a wire line, or a jetting apparatus lowered on a tubing and sealing device 32 may be passed through wellhead isolation tool 68 into production casing 20. Sealing device 32 and perforating device 34 are shown lowered into well 10 as a single tool string on a wire line 36. It is understood that such devices may be lowered separately, and may be lowered on tubing, coiled or jointed, as opposed to wire line 36. Sealing device 32, which may be any number of sealing devices known in the art such as bridge plugs, or packers, is set in well 10 below formation 38 and above formation 25. Perforating device 34 may then be utilized to perforate the additional formation 38 in well 10. Perforating device 34 may then be retrieved and formation 38 may be stimulated with an acidizing or fracturing fluid as known in the art. Such operations can be conducted sequentially in well 10 as many times as desired without the need for removal of the wellhead isolation tool which is more economical and efficient than prior methods. Thus, any desired number of formations may be perforated and treated as described herein without removing wellhead isolation tool 68. While the downhole operation described herein involves sealing the well and perforating at a plurality of locations, it is to be understood that equipment for performing other downhole operations, such as, for example, frac plugs, packers, coil tubing and coil tubing mud motors, drop darts and perforating balls may be lowered through mandrel 72 of wellhead isolation tool 68.

The wellhead isolation tool 68 described herein is a self-aligning isolation tool that is insertable in casing 20 without causing damage to the mandrel 72 or to sealing system 104. As isolation tool 68 is inserted through wellhead 40 and into production casing 20, bow springs 98 will engage wellhead interior 42 and will centralize mandrel 72 so that it will be received in production casing 20 with little or no damage to sealing system 104 and mandrel 72. Prior apparatus which do not utilize a centralizer require a much heavier wall to prevent damage to the mandrel. As such, a more restrictive bore, which does not provide for the passage of service tools, must be used. Tools that seal above top casing 54 do not adequately protect the wellhead. The current invention resolves both issues. Sealing system 104 will sealingly engage inner bore or inner surface 53 of top casing 54 to provide preferably a pressure and fluid tight seal between isolation tool 68 and production casing 20. Because the thin-walled mandrel 72 is centralized, there is little or no risk of damage to the mandrel or the wellhead. Stimulation operations may then be performed as described hereinabove. After stimulation of the well 10, any number of service operations such as setting plugs, perforating and other operations may be conducted with the wellhead isolation tool 68 in place in wellhead 40. The process of stimulating and conducting downhole operations can be repeated as often as necessary, thus alleviating the need for removal of wellhead isolation tools.

Referring to FIGS. 5-7, an additional embodiment of a centralizer apparatus 150 for use in the wellhead isolation tool is shown. Centralizer apparatus 150 comprises a mandrel 152 with a centralizing device 154 slidably disposed thereabout. Mandrel 152 has upper end 156 and lower end 158. Upper end 156 may be attached to mandrel extension 80. Mandrel 152 is preferably a thin-walled mandrel that defines a mandrel bore 160. Bore 160 is an open bore which provides for the passage of service tools and/or coiled tubing therethrough, as with the previously discussed embodiment. The wellhead isolation tool of FIGS. 5-7 will be referred to as wellhead isolation tool 68 a when use with centralizing apparatus 150 is contemplated. Thus, wellhead isolation tool 68 or 68 a may be utilized not only for treatment processes such as fracturing and acidizing, but as explained in detail herein may be left in place when other service operations such as setting plugs and perforating are conducted. Mandrel 152 defines an outer surface 162, with a first or upper groove 164 and second or lower groove 166 defined therein. A shoulder 168 defines a lower end to a first outer diameter 170 defined by outer surface 162. A second outer diameter 172 is smaller than outer diameter 170.

Centralizing device 154 comprises an upper collar 176 and a lower collar 180 and includes a plurality of bow springs 178 extending between and connected to collars 176 and 180, respectively. Bow springs 178 may have first and second end rings 182 and 184, respectively, at the ends thereof. End rings 182 and 184 may be utilized to connect the bow springs to upper and lower collars 176 and 180, respectively. End ring 182 may be spot-welded through openings 186 in upper collar 176. Collar 176 may be attached to bow springs 178 by other means known in the art as well. Likewise, bow springs 178 may be attached by any means known in the art to lower collar 180. Upper collar 176 may comprise a collet that includes a plurality of collet fingers 188. While the centralizing device described herein includes upper and lower collars, other configurations that utilize bow springs may be used, for example, bow springs attached to a collar at only one end.

A sealing system 190 is operably associated with mandrel 152 such that when mandrel 152 is inserted into top casing 54 a seal is created therebetween. Sealing system 190 preferably comprises three separate seals, namely a first or upper seal 192, a second or intermediate seal 194 and a third or lower seal 196. Seals 192, 194 and 196 have outer diameters 198, 200 and 202, respectively. Preferably, diameter 202 is smaller than diameter 200 and diameter 200 is smaller than diameter 198 such that the seals are progressively larger in diameter from the lower end 158 of mandrel 152 in a direction upwardly toward upper end 156 of mandrel 152. Seals 192, 194 and 196 are preferably made of an elastomeric material and may be a swellable material as described herein.

When wellhead isolation tool 68 a is inserted into the wellhead 40, it will be inserted so that sealing system 190 is received in top casing 54. While sealing system 190 includes three seals 192, 194 and 196 of increasing diameter from the lower end 158 toward the upper end 156 of mandrel 152, more or less than three seals may be used and one seal only may be used as well. Shoulder 168 and groove 164 define the limits of axial movement of centralizing device 154. Lower groove 166 is configured so that collet fingers 188 will be received therein and will prevent any further downward movement relative to mandrel 152. Lower groove 166 therefore is lower limit of axial movement for centralizing device 154. Grooves 166 and 168 are configured to allow collet fingers 188 to move upwardly, and upward travel relative to mandrel 152 stops when collar 180 engages shoulder 168.

Bow springs 178 will engage wellhead 40 in wellhead interior 42 to centralize and align mandrel 152 with production casing 20. Mandrel 152 may therefore be inserted in production casing 20 without prematurely engaging any other surfaces in wellhead interior 42. Mandrel 152 will not be damaged in the insertion process, and because the mandrel defines an open bore, and has a thin wall, service tools will pass therethrough. Just as described with respect to tool 68, tool 68 a, when inserted in production casing 20 protects wellhead 40 from not only the high pressure but from the corrosive and/or abrasive effects of the fluids that might be utilized in acidizing or fracturing processes. After the initial formation 25 has been stimulated, it may then be desirable to perforate, stimulate and produce hydrocarbons from one or more additional formations intersected by well 10. The operation described can be performed without the removal of isolation tool 68 a.

Thus, it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims. 

1. A self-aligning wellhead isolation tool comprising: a tubular mandrel having first and second ends; a centralizing device mounted to and extending radially outwardly from the mandrel adapted to engage the wellhead along at least a portion of the interior thereof to align the isolation tool; and a sealing system operably associated with the mandrel, the sealing system operable to seal against the casing bore of a top casing joint in the wellhead to protect the wellhead during treatment of a well.
 2. The wellhead isolation tool of claim 1 wherein the sealing system is mounted on the mandrel, and the mandrel and sealing system are insertable into the top casing to seal against the casing bore.
 3. The wellhead isolation tool of claim 2, the sealing system comprising a generally circular seal disposed about the mandrel.
 4. The wellhead isolation tool of claim 2, the sealing system comprising a plurality of seals disposed about the mandrel, each seal having an outer diameter, wherein the outer diameter of the seals increases from the lower end toward the upper end of the mandrel.
 5. The wellhead isolation tool of claim 4, wherein the sealing system comprises three longitudinally spaced seals disposed about the mandrel.
 6. The wellhead isolation tool of claim 1, wherein the centralizing device comprises: a plurality of bow springs; and first and second collars slidably disposed about the mandrel, the bow springs being attached at first and second ends thereof to the first and second collars.
 7. The wellhead isolation tool of claim 6, wherein one of the first and second collars comprises a collet.
 8. The wellhead isolation tool of claim 7, the sealing system comprising at least one seal disposed about the mandrel, the at least one seal having an outer diameter sized to sealingly engage the casing bore of the top casing joint.
 9. The wellhead isolation tool of claim 1, the mandrel defining a mandrel bore capable of receiving service tools therethrough for conducting downhole service operations in the well.
 10. The wellhead isolation tool of claim 1, further comprising a perforating device positioned in the well, wherein the perforating device is lowered through the mandrel and suspended in the well.
 11. A wellhead isolation tool, comprising: a mandrel defining a flow passage for treatment fluids, the mandrel being insertable into a top casing bore in the wellhead; and a sealing system mounted on the mandrel for sealing against the top casing bore, wherein the sealing system has a progressively larger diameter in a direction from a lower end of the mandrel upwardly toward the upper end of the mandrel.
 12. The wellhead isolation tool of claim 11, the flow passage being defined by a mandrel bore, wherein the mandrel bore is adapted to receive service tools therethrough.
 13. The wellhead isolation tool of claim 11, the sealing system comprising a plurality of seals mounted on the mandrel, the seals having progressively increasing outer diameters from a lowermost seal upwardly to an uppermost seal.
 14. The wellhead isolation tool of claim 11 further comprising a centralizing device for centralizing the sealing system prior to insertion into the casing bore.
 15. The wellhead isolation tool of claim 14, the aligning device comprising a plurality of bow springs disposed about the mandrel.
 16. The wellhead isolation tool of claim 15, further comprising first and second collars slidably disposed about the mandrel, the bow springs being attached at first and second ends thereof to the first and second collars.
 17. The wellhead isolation tool of claim 11, wherein the mandrel defines a mandrel bore having a diameter large enough to accommodate the passage of service tools therethrough, so that well treatment services may be performed without removing the wellhead isolation tool from the wellhead.
 18. The wellhead isolation tool of claim 17, wherein the mandrel bore will accommodate the passage of a tool selected from the group consisting of bridge plugs, packers and perforating devices.
 19. A method of conducting multi-stage operations in a well comprising: deploying a wellhead isolation tool in a wellhead; sealingly inserting a lower end of the wellhead isolation tool into a casing bore of a casing in the wellhead; pumping a treating fluid through the wellhead isolation tool into the well and into a selected zone intersecting the well; lowering a service tool through the wellhead isolation tool; performing a selected service with the service tool; and retrieving the service tool through the wellhead isolation tool.
 20. The method of claim 19, the treating fluid comprising a fracturing fluid.
 21. The method of claim 19, the service tool comprising a perforating device, the performing step comprising perforating casing in the well at an additional selected zone.
 22. The method of claim 21, comprising sequentially repeating the pumping, lowering, performing and retrieving steps for a desired number of selected zones.
 23. The method of claim 19 wherein the service tool comprises at least a perforating device and a well sealing device, the performing step comprising sealing the well below the perforating device, and perforating the well at an additional selected zone.
 24. The method of claim 23 further comprising pumping a treating fluid into the additional selected zone after the perforating step, and repeating the sealing and perforating step in the well at additional selected zones.
 25. The method of claim 19 comprising aligning the lower end of the isolation tool with the casing bore prior to the inserting step.
 26. The method of claim 25, the wellhead isolation tool comprising a centralizing device for centralizing the wellhead isolation tool and aligning the lower end of the wellhead isolation tool with the casing bore.
 27. A method of preparing a well for production comprising: sealingly inserting a wellhead isolation tool through a wellhead at the well into a top casing bore; pumping a treating fluid through the wellhead isolation tool into a selected zone intersecting the well; lowering a tool string including at least a well plug through the wellhead isolation tool into the well; setting the well plug in the well above the selected zone; and perforating the casing adjacent an additional selected zone above the plug in the well without removing the wellhead isolation tool.
 28. The method of claim 27, wherein the lowering step comprises lowering a perforating device through the wellhead into the wellbore along with the well plug on a single tool string.
 29. The method of claim 27 further comprising: pumping a treating fluid through the wellhead isolation tool into the well and through the perforations adjacent the additional selected zone to treat the additional selected zone; lowering a tool string through the wellhead isolation tool, the tool string including at least a well plug; and setting the well plug in the well above the additional selected zone.
 30. The method of claim 27 further comprising sequentially repeating the pumping, lowering, setting and perforating steps upwardly in the well for a desired number of additional selected zones.
 31. The method of claim 30, further comprising aligning the wellhead isolation tool in the wellhead to align a mandrel of the wellhead isolation tool with the top casing bore prior to the inserting step.
 32. The method of claim 30, wherein the treating fluid comprises a fracturing fluid.
 33. The method of claim 27, wherein the treating fluid comprises a fracturing fluid.
 34. The method of claim 27, further comprising aligning the wellhead isolation tool in the wellhead to align a mandrel of the wellhead isolation tool with the top casing bore prior to the inserting step.
 35. The method of claim 34, comprising using a centralizing device mounted on the wellhead isolation tool to perform the aligning step.
 36. The method of claim 27, comprising using a centralizing device mounted on the wellhead isolation tool to perform the aligning step. 